Interbody spinal fusion implants with multi-lock for locking opposed screws

ABSTRACT

An apparatus includes an interbody spinal fusion implant having a leading end, a trailing end, and a length therebetween, and opposed upper and lower portions adapted to contact each of the adjacent vertebral bodies. Each of the upper and lower portions has at least one opening adapted to communicate with one each of the adjacent vertebral bodies and to communicate with one another to permit for the growth of bone from vertebral body to adjacent vertebral body through the implant. Each of the upper and lower portions has at least one screw hole passing therethrough proximate the trailing end. The apparatus further includes bone screws adapted for placement through the screw holes of the upper and lower portions and into each of the adjacent vertebral bodies adjacent the disc space to be fused and into which the implant is adapted to be positioned. At least one lock may be used to prevent the bone screws from backing out of the vertebral bodies and implant.

RELATED APPLICATION

This application claims priority to application Serial No. 60/132,665filed May 5, 1999 and application Serial No. 60/133,214 filed May 7,1999, both of which are incorporated by reference herein.

BACKGROUND

1. Field of the Invention

The present invention relates generally to interbody spinal fusionimplants. Implants, artificial or natural, are placed at least in partwithin a disc space and in contact with each of the vertebral bodiesadjacent that disc space for spacing apart and aligning those vertebralbodies and for allowing for the growth of bone in continuity fromvertebral body to adjacent vertebral body through said implant.

2. Description of the Related Art

Some of the degenerative conditions that affect the spine may be sosevere as to require surgical intervention. For example, a discherniation may compress the spinal cord and/or nerve roots and causepain, loss of function, and even complete paralysis of the legs withloss of bowel and bladder control. The correct treatment for suchconditions is the removal of the offending discal tissue.

Sometimes, for a variety of reasons including the removal of discmaterial, the spine may become unstable (too much motion) at any givenlevel. Historically, this has been treated by fusion, the joiningtogether permanently of the unstable vertebrae via a bridge of bone soas to eliminate all motion along that portion of the spine.

To achieve fusion, bone or bone like substances are applied between two(or more) separate and distinct bones to induce bony bridgingtherebetween. When such procedures are successfully performed betweenvertebral bodies, an interbody fusion results. The shared bone in thearea previously occupied by an intervertebral disc is referred to as aninterbody fusion.

When a spinal surgeon seeks to perform an interbody fusion, the spinemay be accessed from a variety of directions. If the surgeon elects toapproach the spine anteriorly, this generally requires severing and/orremoving substantial portions of the anterior longitudinal ligament overthe operated area. The anterior longitudinal ligament is positionedalong the anterior spinal surface and prevents hyperextension of thespine as an individual bends backward. Because the anterior longitudinalligament covers the anterior spinal surface, the surgeon must cutthrough this tough ligament to access the disc space therebelow,compromising the stability of the spine. Specifically, the anteriorlongitudinal ligament is generally lax, except when an individual leansbackward, then the ligament acts as a tension band resisting elongation.If the anterior longitudinal ligament is damaged, there is no check onthat spinal movement and the vertebral bodies may detrimentallyangulate.

Without a functional anterior longitudinal ligament, the patient maydamage an implant(s) placed into a disc space to facilitate interbodyfusion of the adjacent vertebral bodies. The implant may crush into orerode into, the adjacent vertebral bodies as the disc space opensanteriorly and crushes down posteriorly when the patient bendsbackwards. The vertebrae may rock together posteriorly and openanteriorly, thus dislodging the implant. Accordingly, in at least anyspinal surgery requiring access to the disc space through the anteriorlongitudinal ligament, there is a need to functionally reconstruct theanterior longitudinal ligament to preserve stability about the discspace to be fused. Stability of the spine across the disc space to befused is beneficial for achieving fusion.

In order to perform anterior interbody spinal fusion, a significantamount of disc material is removed from the interspace to be fused.After removing the disc material, the disc space is filled with animplant, which generally includes bone or bone in combination with areinforcing structure, such as an artificial (other than bone) interbodyspinal fusion implant. Because of the forces and motions occurringthrough the spine, it is not uncommon for such implants to dislodge,thereby causing a failure of surgery and possibly warranting furthersurgery to correct the problem and to again attempt interbody fusion.

Metal hardware outside the disc space affixed anteriorly to thevertebral bodies adjacent the disc space to be fused is useful to ensurethe stability of the spine during the fusion period. Those skilled inthe art have shown great reluctance to utilize such hardware because ofthe potential for the hardware to impinge on vital body structures, suchas the aorta, vena cava, or great iliac vessels. The rupture of any ofthese body structures could cause sudden death. A rupture may occur lateafter surgery due to the pulsing of an artery against the metal hardwareresulting in the eventual erosion and rupture of the artery. Further,metal applied to the outer surfaces of the vertebral bodies may becomeloose. For example, a screw may back out from repeated bodily movements,leading to the above-described situation.

Therefore, there is a need for an implant that is resistant todislodgment and functionally substitutes for the anterior longitudinalligament at the level to be fused, without protruding from the spine.

SUMMARY OF THE INVENTION

According to the present invention, an improved interbody spinal fusionimplant is provided. The implant has structure that functionallysubstitutes for a damaged anterior longitudinal ligament following ananterior implant procedure. The present invention is not limited tofunctionally reconstructing the anterior longitudinal ligament, however,and also is useful for increasing the stability of the implant,decreasing the mobility of the adjacent vertebrae to be fused together,increasing and more evenly distributing the compressive loads across thefusion site, and mitigating the generation of undesirable localizedexcessive peak loads; and thus is of great benefit for implants insertedinto the disc space posteriorly or laterally as well as anteriorly.

Existing interbody spinal fusion implants do not adequately addressesthe above described broad needs or the need to functionally reconstructthe anterior longitudinal ligament, which to be useful must be done in away that can assure the safety of the great blood vessels. The presentteachings provide the structure by which implants may be constructed orexisting implants may be modified to take advantage of the improvementsof the present invention.

Implants that may be modified to incorporate the present teaching arethose interbody implants adapted for placement within a disc space ofthe human spine between adjacent vertebral bodies, which implants havesurfaces for contacting each of the adjacent vertebral bodies andstructure therethrough, such as opening(s), to allow for the growth ofbone from vertebra to vertebra through the implant. Such implants, interalia, include generally rectangular implants such as disclosed in U.S.Pat. No. 5,776,199 to Michelson; lordotic interbody spinal fusionimplants such as disclosed in U.S. Pat. No. 5,609,635 to Michelson;threaded cylindrical spinal implants such as disclosed in U.S. Pat. No.5,860,973 to Michelson; thin-walled, perforated, threaded, hollowcylindrical implants such as disclosed in U.S. Pat. No. 5,015,247 toMichelson; and thin-walled, multiperforated partially cylindrical andcylindrical implants such as disclosed in U.S. Pat. No. 5,785,710 toMichelson. U.S. Pat. Nos. 5,776,199; 5,609,635; 5,860,973; 5,015,247;and 5,785,710 are incorporated herein by reference. The presentinvention and any or all of its parts may be constructed out of anymaterial appropriate for the described purpose including, but notlimited to, cortical bone, surgical quality metals, ceramics,bioresorbable and non-resorbable plastics and composites.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a first embodiment of the implant of thepresent invention.

FIG. 2 is a trailing end view of the implant of FIG. 1.

FIG. 3 is a leading end view of the implant of FIG. 1.

FIG. 4 is a side elevational view of the implant of FIG. 1, includingopposed bone screws.

FIG. 5 is a trailing end view of the implant of FIG. 4 with screws andscrew locks installed.

FIG. 6A is a side elevational view in partial cross section of ascrew-lock driver.

FIG. 6B is a side elevational view in partial cross section of thedistal end of the driver of FIG. 6A in accordance with its method of usewith an implant shown as a portion in cross section, bone screw, andlock in cross section.

FIG. 7 is a top plan view of a second embodiment of an implant inaccordance with the present invention.

FIG. 8 is a leading end view of the implant of FIG. 7.

FIG. 9 is a trailing end view of the implant of FIG. 7.

FIG. 10 is a side elevational view of the implant of FIG. 7, includingopposed bone screws.

FIG. 11 is a trailing end view of the implant of FIG. 10 with the screwslocked.

FIG. 12 is a cross sectional side view of an implant rear wall, withopposed bone screws, and a preinstallable lock in the open position.

FIG. 13 is a cross sectional side view of an implant rear wall, opposedbone screws, and with the locking element of FIG. 12 in the lockedposition.

FIG. 14 is a top plan view of a third embodiment of an implant inaccordance with the present invention.

FIG. 15 is a side elevation view of the implant of FIG. 14 with opposedbone engaging screws and screw lock.

FIG. 16 is a leading end view of the implant of FIG. 14.

FIG. 17 is a trailing end view of the implant of FIG. 14.

FIG. 18 is a trailing end view of the implant of FIG. 15 with opposedbone engaging screws and screw lock.

FIG. 19 is a side elevation view of a bone screw lock.

FIG. 20 is a side elevation view in partial cross section through therear wall of the third embodiment implant with the bone screws and screwlock in place.

FIG. 21 is a top plan view of the fourth embodiment of an implant inaccordance with the present invention.

FIG. 22 is a leading end view of the implant of FIG. 21.

FIG. 23 is a trailing end view of the implant of FIG. 21.

FIG. 24 is a side elevation view of the fourth embodiment implant withopposed bone engaging screws.

FIG. 25 is a trailing end view of the implant of FIG. 24 with screws andscrew locks in place.

FIG. 26 is a top plan view of the screw lock of FIG. 25.

FIG. 27 is a side elevation view in partial cross section through aportion of the rear wall of the fourth embodiment implant, with opposedbone screws, and lock.

FIG. 28 is a top plan view of an alternative lock.

FIG. 29 is a side elevation view and partial cross section through therear wall of the fourth embodiment implant with the bone screws andalternative lock of FIG. 28 in place.

FIG. 30 is a top plan view of a fifth embodiment implant in accordancewith the present invention.

FIG. 31 is a side elevation view of the implant of FIG. 30, with opposedlocked bone screws and locks in place.

FIG. 32 is a trailing end view of the implant with screws and locks ofFIG. 31.

FIG. 33 is a leading end view of the fifth embodiment implant.

FIG. 34 is a side perspective view of the fifth embodiment implant.

FIG. 35A is a side elevation view and partial cross section through therear wall of the fifth embodiment implant, with bone screws, and a lockpositioned for engagement with a bone screw.

FIG. 35B is a top plan view of a bone screw.

FIG. 35C is a side elevation view of a bone screw head.

FIG. 35D is a top plan view of a screw lock.

FIG. 36 is a side elevation view and partial cross section through therear wall of the fifth embodiment implant with locks engaged with thebone screws.

FIG. 37 is a top plan view of a sixth embodiment of an implant inaccordance with the present invention, with bone screws.

FIG. 38 is a side elevation view of the sixth embodiment implant withscrews of FIG. 37.

FIG. 39 is a leading end view of the sixth embodiment implant.

FIG. 40A is a trailing end view of the sixth embodiment implant.

FIG. 40B is a trailing end view of an alternative sixth embodimentimplant.

FIG. 41 is a detailed side elevation view in partial cross section of aportion of the rear of the sixth embodiment implant and the bone screw.

FIG. 42 is a detailed side elevation view in partial cross section ofthe rear wall of the sixth embodiment implant and an alternative screw.

FIGS. 43, 44, and 45 are side elevation views in partial cross sectionshowing a portion of the rear wall of one of the embodiments of theimplants of the present invention and an alternative screw and lockmechanism.

FIG. 46A is a side perspective side view of an eighth embodiment of animplant of the present invention.

FIG. 46B is a side perspective view of a ninth embodiment of an implantof the present invention.

FIG. 46C is a side elevation view of the implant of FIG. 46A.

FIG. 46D is a trailing end view of the implants of FIGS. 46A and 46B,properly inserted within a spine.

FIG. 46E is a side elevation view in partial cross section, showing theformation of a generally cylindrical bore across a disc space in aspine.

FIG. 46F is a top plan view along line 46F—46F of FIG. 46D.

FIG. 47A is a side elevation view in partial ghost of a screwdriver foruse with the self-locking screw of FIGS. 48 and 49.

FIG. 47B is a bottom end view of the distal portion of the driver ofFIG. 47A.

FIG. 48 is a top plan view of the head portion of a self-locking screwof FIG. 49.

FIG. 49 is a side elevation view of the self-locking screw of FIG. 48.

FIGS. 50, 51, 52, and 53 are side elevation views in partial cutawayillustrating the method of use of the driver of FIGS. 47A and 47B andthe self-locking screw of FIG. 49 in relation to the ninth embodiment ofthe present invention properly inserted in a spine.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention relates first to implants to be placed within ahuman spine, at least in part, within a disc space between adjacentvertebral bodies, for the purpose of fusing together those two adjacentvertebral bodies across the intermediate disc space. Though not solimited, it is desirable that these implants allow for the growth ofbone from vertebra to adjacent vertebra through the implants themselves.To this end, each implant, when inserted, will have an upper implantsurface for engaging the upper of the adjacent vertebral bodies and anopposed lower implant surface for engaging the adjacent lower vertebralbody. It is desirable that each of these opposed surfaces has at leastone opening, and possibly a plurality of openings, sufficient in size,and in continuity with each other, to allow for the growth of bone fromvertebral body to adjacent vertebral body through said implant. Whilenot requisite, it is also desirable that these implants further behollow to facilitate such bone growth through the implant.

The implants of the present invention differ from all prior art implantsin that they are adapted to receive through their trailing ends at leasta pair of appropriately sized opposed bone screws that can be directedat an appropriate angle, at least one each, into each of the adjacentvertebral bodies adjacent the disc space to be fused. In a further novelteaching of the present invention, these implants adapted to receive theopposed bone screws are further adapted also to receive bone screwlocks, or in the alternative the screws are adapted to receive locks tolock the screws to the implants to prevent the backing out of the bonescrews from the implants.

To the extent that such implants are hollow and have openings throughthe surfaces, those openings and those hollows can preferably be filledwith fusion promoting substances, including substances that areosteogenic, osteo-inductive, or osteo-conductive, whether naturallyoccurring, or artificially produced. Such substances could include, butare not limited to, bone in any of its forms, whether naturallyoccurring or processed, hydroxyapatite, calcium phosphate compounds,bone morphogenetic proteins, and genetic materials coding for theproduction of bone. Various embodiments of the present invention showimplants having a large hollow therein. While not requisite, it may beadvantageous to have a large access-way to the implant hollow. By way ofexample, a cap may be used for closing all or part of the access-way.

The present invention implant including the screws and locks may beformed of any material suitable for their intended purpose. To that end,they can be made of a surgical quality metal such as titanium or one ofits alloys, cobalt chrome, or any other surgical quality metal suitablefor the intended purpose. The implant can be made of an appropriateceramic, be it naturally occurring or artificially produced. The implantalso can be formed of or include cortical bone. The implant can beformed of plastics or composites, for example, a carbon fiber plasticmaterial or bioresorbable material. The implant can further comprise orbe filled with, treated with, coated with, or used in combination withvarious fusion promoting substances, including but not limited tohydroxyapatite, calcium phosphate compounds, bone morphogeneticproteins, genetic materials coding for the production of bone, and achemical substance to inhibit scar formation.

Shown in FIGS. 1 through 5 is a first embodiment of the presentinvention. Generally cylindrical, highly perforated, hollow interbodyspinal fusion implant 100 has a leading end 102 and a trailing end 104.Leading end 102 has a threadable cap 112 having a drive aperture 114,and holes 110 for the through growth of bone and vascular access. Attrailing end 104 is a box-like recess 118 for receiving an implantdriver (not shown). Trailing end 104 of implant 100 also has a pluralityof bone holes 110 and two more specialized openings 120 which arethreaded for receiving a complimentary threaded member from a driver soas to allow the driver to rigidly affix to trailing end 104 of implant100. Trailing end 104 also has bone screw receiving holes 130, whichadditionally could be used to receive an implant driver. It can readilybe appreciated that the trailing end of this implant or any implantembodiment of the present invention in general can be adapted in amultitude of ways for cooperatively receiving an implant driver to makepossible the insertion of the implant into a spine.

Implant 100 has an upper surface 106 and an opposed lower surface 108,each being adapted for placement into contact with one of the twoadjacent vertebral bodies adjacent a disc space to be fused. Upper andlower surfaces 106 and 108 each have a plurality of openings 110 for thethrough growth of bone. The present invention includes any number orarrangement of openings so long as sufficient to work for the intendedpurpose. Upper and lower surfaces 106 and 108 also have an opening 134and 136, respectively, for allowing the passage therethrough of a bonescrew for further attaching implant 100 to each of the adjacentvertebral bodies. Openings 134, 136 are preferably shaped and formed soas to facilitate the insertion of bone screws 142 through the rear ortrailing end 104 of implant 100 and in part through openings 134, 136.The heads 156 of screws 142 do not pass completely through openings 134,136. Screws 142 pass out of implant 100 preferably at an angle ofbetween 25° and 75° to the long axis of implant 100.

Opposed vertebral body engaging screws 142 are illustrated as having thepreferred, but not requisite, cancellous-type thread 148 and a pointedtip 144 with cutting flutes 146 so as to allow screws 142 to beself-tapping. While any screw useful for the intended purpose iscontemplated to be within the scope of the present invention, aself-tapping screw with a cancellous-type thread pattern over asignificant portion of the shaft, with a smooth shaft proximallycorresponding to the portion within the implant, and a head that can belagged against the implant is particularly preferred for its advantages.The screw head 156 has a drive recess 154, here shown as a hexagon.

FIGS. 6A and 6B show a driver 176 for use with the first embodiment ofthe present invention. Driver 176 comprises a handle 178, having anupper handle portion 179 and a lower handle portion 181. Upper handleportion 179 is attached to a central shaft 180 which terminates in a hexdrive tip 184. Shaft 180 passes coaxially through handle 178 whichextends downward to form a second shaft 182 that houses shaft 180 andterminates distally in a second hexagonal tip 183. An annular groove 175in shaft 180 receives a ball and spring detent 177 to hold handle 181and contiguous shaft 182 in selective position relative to handle 179and contiguous shaft 180.

As can be appreciated from FIG. 6B, in use hexagonal driver tip 184 ofshaft 180 is utilized to insert through the trailing end 104 of implant100 bone screw 142 by means of a hex depression 154 in bone screw head156. Once screw 142 is fully inserted through the opening 130 intrailing end 104, the enlarged portion of the head 156 is blocked frompassing fully through implant 100 by a retaining flange 138 of theimplant. At this point, it is possible to cause the vertebral body intowhich the threads of screw 142 are implanted to be lagged towards, thatis to be compressed to, the implant surface and particularly towardstrailing end 104 of implant 100 by further rotating screw 142. Once theoptimal compression has been obtained as determined by the surgeon atthe time of surgery, with tip 184 of shaft 180 still engaged with screwhead 156 within depression 154, the surgeon then utilizes shaft 180 as acentering post and separates handle portion 181 from handle portion 179by pressing downward. This downward pressure causes the detent ball andspring 177 to be forced out of annular groove 175 and allows secondshaft 182 to move downward, taking with it lock 162 which was engaged todriver 176 prior to engaging driver 176 to bone screw 142.

Lock 162 is circumferentially threaded with threads 172. When secondshaft 182 is advanced distally along shaft 180, lock 162 contactstrailing wall 104 of implant 100, such that threads 172 of lock 162 canbe threaded into the receiving threads 140 of implant 100. In thisexample, it can be appreciated that opening 130 is not fully threadedfor its entire depth, but only sufficient to allow lock 162 to becomegenerally flush with trailing wall 104, at which point lock 162 can bequite rigidly tightened against the unthreaded portion of opening 130,which acts as a stop, preventing any further movement of lock 162 intoopening 130. By binding lock 162 to trailing wall 104 of implant 100 andmaking lower surface 174 of lock 162 concave, allowance is made formotion of screws 142 relative to implant 100. This allows the surgeonsome freedom of choice in positioning screws 142 and in selecting thedirection of the force vector to be generated relative to implant 100.It further allows for some settling of the vertebrae should that occurover time without the danger of the screws acting to hold the vertebraefrom implant 100.

Alternatively, by any number of structural configurations, such as byway of an example an interference fit between screw head 156 and implantopening 130, or by way of more deeply threading the opening 130, or byflattening the top of the screws and making the circumferentialperimeter flush to the lock, or by allowing the lock to contact thescrew head, later motion of the screw can be prevented. Saiddifferently, while the present example shows how to allow forvariability in the screw's placement and provides for later movement ofthe screw as might occur with settling, in the alternative, the path ofthe screw through the implant can be rather narrowly defined, and anyangular motion of the screw relative to the implant can be prevented.

FIGS. 7 through 13 show a second embodiment of the present invention.Implant 200, though similar to implant 100, differs from implant 100 inthat the sides have been tangentially removed and the remaining upperand lower arcuate portions have been wedged apart, such that trailingend 204 is taller than the leading end 202. The tangential truncation ofthe sides allows two implants 200 to be placed side-by-side, such thatthe combined width of the two implants is significantly less than thecombined height of the implants.

The convergence of upper and lower surfaces 206, 208 from trailing end204 to leading end 202 is beneficial for inducing lordosis when implant200 is inserted across the disc space between two adjacent vertebraefrom anterior to posterior. Without in anyway departing from the presentinvention, the implants shown herein by way of example only, can bemodified for posterior insertion, in which case the upper and lowersurfaces may be generally convergent from the leading end to thetrailing end.

Implant 200 has a leading end 202, having a plurality of holes 210therethrough for the through growth of bone and vascular access. Implant200 does not have a removable cap as did implant 100, relying rather onlarge opening 224 which may be present on each side, or one side only toprovide access to the hollow interior 226 of implant 200 for the purposeof loading implant 200 with fusion promoting substances. The implantupper and lower surfaces 206 and 208, respectively, each have at leastone and preferably a plurality of bone holes 210, and similar to implant100, a series of forward facing annular ratchets for engaging thevertebral bone. Upper surface 206 and lower surface 208 have openings234 and 236, respectively, for conducting therethrough bone engagingscrews 242. When implant 200 is implanted, screws 242 are introducedthrough trailing end 204 of implant 200. Trailing end 204 has a pair ofopposed bone screw receiving holes 230 angled so as to direct screw 242introduced through trailing end 204 of implant 200. Holes 230 receivescrew 242, which passes therethrough and into each of the adjacentvertebral bodies. Screw 242 preferably is at an angle to thelongitudinal axis of implant 200 and more preferably at an angle of from25° to 75°. Implant 200 has a plurality of bone holes 210. Situatedintermediate to opposed bone screw receiving holes 230 is a lock 262having a head portion 256 with a hex well 264 therein, and opposedconcave portions 272. It should be understood that various driverengaging structures useful for the intended purpose are anticipated andwithin the scope of the present invention.

As shown in FIGS. 9 and 12, when lock 262 is one-quarter turn short ofbeing fully tightened, openings 230 are fully open for receiving opposedbone screws 242.

As shown in FIGS. 11 and 13, once opposed bone screws 242 have beeninstalled, lock 262 can be further tightened by turning it 90 degreesuntil head 264 bottoms out against implant trailing end 204, therebyallowing the locking screw to be solidly tightened to implant 200.

In FIGS. 9 through 13, it can be seen that a pair of bone screws 242 canbe inserted through openings 230 in trailing end 204 of implant 200,such that heads 256 of screws 242 are restrained within implant 200 bythe contact of the enlarged head 256 against flange portion 238 ofimplant 200. Threaded shaft 268 of lock 262 threads into the rear ofimplant 200.

It can be noted in FIGS. 11 and 13 that while screws 242 have freedom tomove closer together to allow for settling, screws 242 cannot back outof implant 200 with lock 262 in place. As previously discussed, whilethis is considered preferable, implant 200 can be so constructed toprevent any angular freedom of screw 242 relative to implant 200.Further, implant 200 and lock 262 can be configured to cooperate toprevent any backward motion of screw head 256.

FIGS. 14 through 20 show a third embodiment of the present invention.Implant 300 is generally cylindrical and hollow with a thin outer wallthat is highly perforated and carries a helical thread. This particularthread configuration is offered by way of example only, and theinvention anticipates and includes any thread suitable for the intendedpurpose. Further it is understood that a thread can be so formed that itbecomes difficult to define the thread from the outer wall, such thatthe outer surface of the implant is, in essence, the peaks and valleysof the thread. It is further understood that while the thread shown hereis generally continuous and helical, the thread also could beinterrupted.

Implant 300 has a leading end 302 having a threadable cap 312 with aplurality of bone holes 310 and a central hex aperture 314 for receivinga driver. Alternative embodiment implants may be open at their leadingends, trailing ends, or both, or may be closeable or partially closeablewith other than a threaded cap. Implant 300 has an upper bone engagingsurface 306 and an opposed lower bone engaging surface 308. Intermediateupper and lower surfaces 306 and 308, implant 300 has side surfacesidentical to surfaces 306 and 308. Each of these four surfaces have anopening such as 334 and 336, allowing for the passage of bone screw 342therethrough. This arrangement allows for implant 300 to be insertedinto the implantation site by being threaded into the spine until fullyinserted and then properly aligned by quarter-turn increments. Asimplant 300 is advanced with every one-quarter turn, there is theopportunity to properly align a pair of opposed bone screws 242 throughupper and lower surfaces 306 and 308. It can be appreciated that implant300 is highly perforated with a multitude of holes 310, situated overeach of the implant surfaces, though as few as one adequately sized holeper surface could suffice.

With attention to FIGS. 17 and 18, it can be appreciated that trailingend 304 of implant 300 has a threaded central aperture 320 locatedwithin a partially rectangular recess 318 for threadably engaging animplant driver adapted to interdigit and to threadably connect theretofor rotating the implant, both clockwise and counterclockwise whilesimultaneously either pushing or pulling as desired by the surgeon.Trailing end 304 has four symmetrically disposed bone screw receivingholes 330. Once a pair of opposed bone screws 342 have been insertedthrough trailing end 304 of implant 300 and into the adjacent vertebralbodies and sufficiently tightened, lock 362 is inserted into threadedaperture 320 by means of a driver placed into hex well 364 and thentightened down to the back of implant 300. A pair of unused bone screwholes are then available as bone holes similar to 310. FIG. 19 shows thestructure of lock 362 having an enlarged head portion 366, a threadedshaft 368, and a shoulder 372 to allow lock 362 to be tightened againstimplant 300.

FIG. 20 shows lock 362 in use, where it can be appreciated that headportion 352 of screw 342 is prevented from passing through implant 300by retaining flange 338 at the base of hole 330. It can also beappreciated that when lock 362 is fully tightened, portion 372 of head366 can be tightened against implant 300 itself so as to, as previouslydescribed, allow for some convergent motion of the bone screws in theevent of vertebral settling.

FIGS. 21 through 29 show a fourth embodiment of the present invention.Implant 400 has a convex leading end 402 and an opposite trailing end404, here shown as having a generally straight mid-portion with radiusedjunctions to the side walls of implant 400. In the alternative, trailingend 402 of implant 400 could be generally convex and, still further,could be curved so as to generally conform to the contour of theanterior vertebral body in order to sit in close approximation thereto,without the need to be significantly recessed. In another alternative,trailing end 402 could be curved so as to extend significantly beyondthe anterior cortical margins of the vertebral bodies to be fused.

Both leading end 402 and trailing end 404 of implant 400 are highlyperforate to allow for vascular access to hollow interior 426 of implant400, and to allow for the growth of bone therethrough. While the presentinvention does not require the presence of such openings, these openingsare considered highly desirable. Any variation in particularconfiguration of such openings, or their arrangement, and number, solong as useful for the intended purpose, are also within the scope ofthe present invention. Implant 400 has opposed upper and lower vertebralbody engaging surfaces 406 and 408, respectively, which preferably havesurface irregularities serving to both increase the surface area of theimplant and the ability of the implant to engage the adjacent vertebralbodies, thereby enhancing their stability. Implant upper and lowersurfaces 406 and 408 have large windows or slots 424 therethrough, eachin communication with the central hollow chamber 426 of the implant andeach forming a direct path to its counterpart on the opposite surfacethrough implant 400.

As shown in FIGS. 23 and 25, trailing end 404 of implant 400 has, inaddition to the plurality of bone holes 410, two specialized commonholes 428, each containing two further holes 430. Each of holes 430 isadapted to receive a bone screw 442 through trailing end 404 of implant400 at an angle such that the bone screw would be directed first throughtrailing end 404, then through either one of upper or lower vertebralbone engaging surfaces 406 and 408 of implant 400, and finally into thevertebral body itself at an angle preferably between 250 and 750. Holes430 and common hole 428 are angled apart so as to assure that a pair ofbone screws 442 inserted therethrough will be directed one each intoeach of the vertebral bodies adjacent the disc space containing implant400. Trailing end 404 also has a central threaded aperture 420 forreceiving a threaded member for cooperatively engaging an implantdriver. Other ways of coupling the implant and implant driver can bereadily anticipated and are within the scope of the present invention.

As can be appreciated from FIG. 25, trailing end 404 of implant 400 isadapted to receive a total of four bone screws 442 deployed in upwardlyand downwardly projecting opposed pairs, and further to receive intocommon holes 440 threaded lock members 462, preventing screws 442 frombacking out.

As can be appreciated from FIG. 24, implant 400 has a height greater atits trailing end 404 than at its leading end 402, such that the implantitself is lordotic, or capable of inducing a lordotic angulation betweenadjacent vertebral bodies when inserted into the spine from an anteriorto posterior approach. The present invention also includes such implantswhere the upper and lower surfaces 406 and 408 are parallel rather thanconvergent and, still further, where the upper and lower surfaces 406and 408 are divergent from the trailing end to the leading end, for usefrom a posterior to anterior approach.

When the implant as shown in FIG. 24 is inserted from anterior toposterior between the adjacent vertebral bodies, any tendency forimplant 400 to back out of the implantation site created across the discspace due to the wedge-shaped contour of the implant is resisted by boththe forward facing ratchetings 422 and the trajectory of screws 442.Bone screws 442 further serve to pull the vertebral bodies to upper andlower implant surfaces 406 and 408 so as to increase the compressiveload thereon and mitigate against a loss of that compressive load or adistraction anteriorly which might otherwise occur if a patient were tobend back and forth or otherwise extend. Consistent with the preferred,highly perforate nature of implant 400, the side walls of the implantalso have holes 424 therethrough to allow for vascular access and thethrough growth of bone.

FIGS. 26 and 27 show details of holes 430 through trailing end 404 ofimplant 400 in relation to lock 462 and a pair of opposed bone screw442. In this example, bone screws heads 452 are sufficiently large thatthey are not able to pass through flange 438 and are thereby retainedwithin the rear portion of implant 400. Immediately distal to heads 452of screws 442 is a smooth shaft portion 450 of a lesser cross sectionaldimension than hole 430 which, in combination with the available spacewithin common hole 428 between screw head 452 and lock 462, allows forbone screw 442 to operate as a lag screw, but, nevertheless, be capableof some variability in its positioning and ability to move closer toimplant 400 in the event of subsequent settling of the vertebral bodiestowards implant 400. In this embodiment, lock 462 takes the form of adisc with a threaded side wall 472, capable of threadably engagingthreads 472 within common hole 428. Lock 462 comprises a hex receivingopening 464 for rotationally driving lock 462. In a preferred variation,hex opening 464 or other equivalent driver receiving configuration, isthe same as that of head 452 of screw 442.

Turning now to FIGS. 28 and 29, an alternative implant screw and lockarrangement is demonstrated for use with implant 400, or as with thelock and screw configuration of FIG. 27 with any of the otherembodiments of the present invention as may be appropriate. To that end,it should be appreciated that the implants shown herein are by way ofexample only and without limitation to the various combinations andpermutations of the various screw, lock, and implant configurationsshown, as well as the substantial equivalent thereof which areanticipated and claimed to be within the scope of the present invention.

Lock 461 differs from lock 462 in that extending from head portion 463is a threaded shaft 468 for threading into a threaded hole betweenopposed holes 430 within common hole 428 of implant 400. Unlike themechanism illustrated in FIG. 27 where cap 462 tightens against theinternal implant wall rather than locking against the screw headsthemselves, thereby permitting motion, head 463 of lock 461 tightensagainst heads 452′ of screws 442′. Screws 442′ differ from screws 442 inthat the smooth proximal shaft portions 450′ are adapted to form aninterference fit with the passageway through the rear portion of implant400 and thereby allow the screws to have a precise trajectory whilebeing rigidly locked to the implant. It should be appreciated then thatFIGS. 27 and 29 each teach a structure by which an implant of thepresent invention can be constructed so as to either cause the screwspassing therethrough to have a fixed trajectory or a variable angleplacement. Further taught is structure for permitting implants to eitherallow for, or to prevent post-deployment angular motion of the bonescrews relative to the implant after the screws have been lockedtherein; or to allow for but one degree of freedom of the locked screwsfor the settling or the coming closer together of the adjacentvertebrae. Various ways of achieving such structures are shown hereinand may be combined in various ways with various embodiments of theimplants shown or their substantial equivalents without departing fromthe scope of the present invention.

FIGS. 30 through 36 show a fifth embodiment of the present invention.Implant 500 is an improvement upon the implants described in pendingMichelson U.S. application Ser. No. 09/106,216 incorporated herein byreference. These implants have been adapted to have bone screw receivingholes 530 in posterior walls of trailing end 504 and, in each of theopposed upper and lower surfaces 506 and 508, respectively, holes 534and 536 for transmitting bone screws therethrough, respectively.Trailing end 504 also comprises a rectangular slot 518 for engaging arectangular member of an implant driver insertable therein. A threadedhole 520 located within slot 518 allows the implant driver to further besecured to the implant by threadably engaging the implant therethrough.This allows the implant, when properly engaged to the driver, to berotated either clockwise or counterclockwise and simultaneously bepushed or pulled at the discretion of the surgeon.

While not requisite, in a preferred embodiment, implant 500 is highlyperforate and has holes 510 for vascular access and bone through growththrough its leading end 502, side walls, and upper and lower surfaces506 and 508. While trailing end 504 is herein shown lacking additionalbone holes, this has been done to emphasize that such openings are onlypreferred, not requisite. As herein before stated, the particular shape,number, and arrangement of the holes are all within the scope of thepresent invention so long as they are appropriate for their intendedpurposes.

Leading end 502 of implant 500 is herein shown with a cap 512, which isthreaded and removable, and can be operated by a driver engaging hexopening 514. Cap 512 can be removed so that the hollow interior 526 ofimplant 500 can be compressibly loaded with bone. Cap 512 can then bescrewed to the leading end 502 so as to prevent the gross extrusion ofthe osteogenic materials loaded under pressure within the implant while,nevertheless, providing for vascular access to the interior of theimplant and bone growth therethrough. Further, cap 512 may providestructural reinforcement to the implant so as to provide enhancedstrength.

Upper and lower surfaces 506 and 508 of implant 500 have a series oftransverse fins 522 and interposed therebetween a plurality of boneslots and bone holes 510 for the growth of bone therethrough. Implant500 as is described in co-pending U.S. application Ser. No. 09/106,216is adapted to be inserted on its side and then, only after being fullyinserted, rotated 90 degrees so that upper and lower surfaces 506 and508 engage each of the adjacent vertebral bodies adjacent the disc spacein which the implant has been implanted for fusion. Once implant 500 hasbeen properly inserted, bone screws 542 are inserted through opposedholes 530 in trailing end 504 and through holes 534 and 536 in upper andlower surfaces 506 and 508, respectively, with one each passing intoeach of the vertebral bodies. As with various of the other embodimentsof the present invention it is anticipated that the trailing ends ofsaid implants need not have a trailing wall, but rather a generalizedopening without departing from the scope of the present invention.

As shown in FIGS. 35A-36, bone screws 542 have a head 552 and at least apartially, cancellously threaded shaft which is longitudinally cleavedto form an expansion slit 560. Screws 542 may be self-tapping. It may bealternatively beneficial to pre-drill an appropriate opening with adrill placed through the implant and into the vertebral body forreceiving screw 542. When screw 542 has been fully inserted, head 552 isprevented from further motion forward by retaining flange 538, and it isthen possible to generate a compressive lag of the vertebral bodyagainst implant 500 with screw 542. A locking member 562, having asmooth shaft 568 terminating distally in tip 572 is then insertedthrough the drive opening in head 552 of screw 542 until portion 566 oflock 562 threadably engages within head 552. Then as lock 562 isthreaded more deeply into head 552 of screw 542, point 572 wedges aparta conically tapered recess in the shaft of screw 542, thereby wedgingapart the two portions of the shaft.

FIG. 35B is a top view of bone screw 542 of FIG. 35C. FIG. 35 shows thecrossed or Phillips type driver receiving structure of one preferredembodiment of the present invention. A central opening in screw 542 isadapted to receive lock 562. FIG. 35D is a top view of lock 562 andshows a hex configuration of one preferred embodiment of the presentinvention for receiving a driver.

In FIG. 36, the opening of slot 560 is exaggerated to be more useful indemonstrating the function of this particular embodiment. Screw 542 maybe constructed so as to take advantage of a proximal thread portion orother enlargement beyond the root diameter of the proximal shaft whichcan be utilized to form a lock against rearward migration of the screwas it contacts retaining flange 538. With or without such a feature,screw 542 can also rely on its spreadable nature to prevent backwardmigration of the screw. Other variations on this theme, such as the useof a screw with an expandable casing, or any type of expandable screware clearly within the scope of the present invention, as are screwshaving a hollow head and shank portion for transmitting therethrough asecond element which is designed to protrude from the screw at an angleand therefore lock the screw in place.

FIGS. 37 through 42 show a sixth embodiment of the present invention.Implant 600 may generally be round or oblong or comprised in the topview of both arcuate and linear portions, or arcuate portions ofdiffering arcs of radii. In one variation of implant 600, upper andlower vertebrae engaging surfaces 606 and 608, respectively, are but theend surfaces of the perimeter wall of the implant itself. While upperand lower surfaces 606 and 608 could be generally parallel from leadingend 602 to trailing end 604. In a preferred embodiment, trailing end 604of implant 600 is taller than leading end 602 of implant 600, such thatthe opposed upper and lower surfaces 606 and 608 are converging from thetrailing end to the leading end. This offers the advantage that whenimplant 600, which is adapted for insertion from anterior to posterioror from a position anterolaterally, is inserted, the end of the implantthat will face posteriorly will be of a reduced height. This makes theinsertion of the implant into the space from anterior to posterior mucheasier as less initial distraction of the disc space between theadjacent vertebrae is required. Further, having opposed upper and lowersurfaces 606 and 608 diverge from leading end 602 to trailing end 604allows for further restoration of the normal lordotic angulation throughthe disc space between the adjacent vertebrae to be fused.

Implant 600 has a plurality of holes 610 located through its perimeterwall to allow for the growth of bone and vascular access therethrough.Implant 600 has a large central hollow 626 for containing fusionpromoting substances such as bone and for allowing the fusion ofvertebrae to adjacent vertebrae through the implant through area 626 andthrough the disc space. Implant 600 is adapted to receive opposed bonescrews 642 for engaging each of the vertebral bodies adjacent the discspace into which the implant is implanted.

As shown in FIG. 40A, trailing end 604 of implant 600 has common holes628 having opposed bone screw receiving holes 630. Holes 630 are notonly angled away from each other so as to face at an angle to theopposed upper and lower implant surfaces, but are further angled towardsthe midline of the implant as shown in FIG. 37.

FIG. 40B shows trailing end 604′ of implant 600′, which is a bone ring,such as a femoral ring of cortical bone. Trailing end 604′ has bonescrew receiving holes 630 a-630 d for receiving bone screws 642 therein.Bone screw receiving holes 630 a′ and 630 d′ are oriented toward lowersurface 608′ for engaging a vertebral body above implant 600′. Opposedbone screw receiving openings 630 b′ and 630 c′ are oriented towardupper surface 606′ for engaging a vertebral body below implant 600′.Accordingly, it is appreciated that as used herein the term “opposed” isnot limited to being diametrically opposed, but includes opposite facingscrew holes that are offset from one another. Preferably as describedherein a lock or locks are provided to retain the screws when passing atleast in part, and retained at least part through the openings.

As shown in FIGS. 41 and 42, holes 630 in a preferred embodiment havethreaded walls 640. In a first example as shown in FIG. 41, bone screw642 has a head portion 652 having a threaded portion 658 for threadablyengaging the threaded wall 640 in hole 630 of implant trailing end 604.Screw head 652 also has an enlarged head portion 654 incapable ofpassing through the threaded portion of hole 630 and further allowingfor bone screw 642 to be securely tightened down to and against theimplant, thereby locking it to the implant.

FIG. 42 illustrates an alternative design for a self-locking screw as avariation to that shown in FIG. 41. Screw 642′ has a hex drive 654similar to screw 642. Also like screw 642, screw 642′ has a threadedshaft 648 and a threaded head portion 658′. However, unlike screw 642,screw 642′ does not have an additional enlarged head portion such asportion 654 of screw 642, but rather relies on flange portion 638 ofopening 630 to stop the further progression of the screw head 652′through the implant and allow for head 652′ to be securely tightened tothe implant trailing end 604.

As a further alternative to both screws 642 and 642′ being rigidlysecured to implant 600 and resistant to any angular motion thereto, thetrailing end of the implant includes a rotatable bearing having athreaded passageway therethrough and externally, at least in part, acurved profile allowing for the bearing to be trapped within rear wall604 of the implant while still leaving it free to rotate within acomplimentary socket formed therein. Because the screw threadablyengages within the bearing, which is trapped within the rear wall of theimplant it can be securely tightened to the bearing while yet stillbeing free to move. In an alternative design, the bearing has slits andthe screwhead, upon final tightening, expands the bearing so that itpresses against the bearing retaining socket of the rear wall, lockingthe screw-bearing complex to the back of the implant to the extentdesired. In a further variation of the 642 type screw the head mayslightly flare outward from distal to proximal withexpansion/compression slots therethrough allowing the head to be selflocking within the threaded opening of the implant or a bearing asdescribed above.

FIGS. 43 through 45 show an alternative embodiment of a locking screwmechanism which can be adapted for use with various of the other shownand/or described implant embodiments of the present invention. Trailingend 704 of an implant 700 has a hole 730 for accepting a bone screw 742.Bone screw 742 has a head portion 752 having at least a part about itsperimeter a convex surface 756 having a maximum diameter. Bone screwreceiving hole 730 has a circumferential concavity portion 748 forreceiving convexity portion 756 of the bone screw head. Bone screw head752 has internal threads 758 and a plurality of slots 760, preferablyfour. Slots 760 allow screw 742 to be driven with a cruciate type driverand allow for head 752 to sufficiently compress to be fully receivedwithin hole 730 of the implant. It can be appreciated from FIGS. 43through 45 that screw 742 can be placed at an angle to the implant 700.Further, once the bone screw has been fully engaged into the adjacentvertebral body, the screw can be further rotated, allowing the vertebralbody to be lagged to the implant, increasing the compressive load. Oncea screw has been properly placed and tightened to the extent desired bythe surgeon, a locking screw 762 having a head 766 and a threaded shaft768 may be threaded into the threaded interior of the head 752 of bonescrew 742. The implant screw locking system of FIGS. 43 through 45 canbe manufactured such that while the locking screw 762 may be lockablytightened to the bone screw 742, and thus the backward migration of 742from the implant prevented, the system can be designed so as to eitherallow for angular motion after the locking screw 762 is locked to thebone screw 742 or to prevent it. The function of the head in its abilityto rotate and angulate within the implant is not dissimilar to the abovedescribed variation of the self locking screw and rounded bearingcombination.

FIGS. 46A through 53 show an eight and ninth embodiment of the presentinvention. Implants 800 and 900, which are shown in FIGS. 46A-46C can beused by themselves, or with a second of their kind, or as acomplimentary pair as well shown in FIGS. 46D and 46F.

FIGS. 46A-53 show implants 800 and 900 and a series of steps useful fordiscussing a method of use of the present invention implants. Methodsfor inserting spinal implants are discussed in part in issued andpending patent applications to Michelson U.S. Pat. Nos. 5,593,409,5,741,253, 5,484,437, Ser. Nos. 08/396,414, and 08/480,904, incorporatedherein by reference. The disc space to be used is preferably, but notnecessarily, distracted to optimal height and the vertebral bodiespreferably, but not necessarily, properly aligned. A pair of overlappingbores, as best illustrated in FIG. 46D, are then formed across the discspace with a bone removal device, as shown in FIG. 46E. The bone removaldevice is preferably a drill having a diameter greater than the heightof a distracted disc space such that arc-shaped portions of bone areremoved from each of the vertebral bodies adjacent the disc space to befused. The overlapping bores are generally oriented from anterior toposterior and preferably stop short of the spinal canal.

A bone removal device such as a drill or mill that may be conical can beutilized to complement the tapered configuration of the implant body. Asshown in FIG. 46E, however, in a preferred method a generallycylindrical drill DR or end mill is utilized to create a generallycylindrical bore “B” for receiving the implants. When a pair ofgenerally cylindrical overlapping bores, preferably but not necessarily,having a diameter generally corresponding to that of the root diameterof the implant proximate the leading end are formed as per. FIG. 46D,the implants will come to be positioned such that the combined width ofthe implants at their leading ends will be less than the combined widthof implants at their trailing end. That is, the implants will be angledin towards each other from anterior to posterior. This has the furtherbenefit of swinging the junction of the lateral side walls and trailingends further inward and away from escaping the anterior vertebralcortex, thereby avoiding protrusion of the lateral side wall to trailingend junctions and allowing for the installation of larger and longerimplants than might otherwise be possible.

As has been taught by Michelson in the above identified applications andpatents incorporated by reference herein, the disc space may bedistracted in any number of ways and held distracted during the boreformation portion of the procedure. Some of the preferred ways includethe use of long distractors, short distractors, and extended outersleeves having distractor members for placement within the disc spaceand between the adjacent vertebral bodies as described by Michelson inthe above described applications and patents incorporated by referenceherein. Other distractors such as those which attach to the vertebralbodies as by pins or screws might also be useful for the presentintended purpose.

While surgery may be performed through a single bore first, in apreferred embodiment both bores are created in overlapping fashion priorto the insertion of the first implant which in this example is implant800. Implant 800 is affixed to an implant driver, which preferablyengages the implant at trailing wall 804 by interdigitating with implant800 and further binding to implant 800 by a thread such that it ispossible both to rotate implant 800 in either direction and to push orpull simultaneously. While that may be achieved by having a driver whichinterdigitates with any of the openings into or through rear wall 804and having a rotatable portion for threading into threaded opening 820the present invention is not so limited and may include any driveruseful for the intended purpose.

After implant 800 is fully seated with the medial side wall orientedimmediately toward the disc space, a complementary implant 900 isinserted by allowing it to rotate within the maximum circumference ofimplant 800. Pre-tapping the bores formed across the disc space prior tothe insertion of the implants does not deviate from the presentteaching. In a preferred embodiment, pre-tapping is not required ascertain preferred embodiments of the present implants are tapered fromtheir trailing to their leading ends and the leading ends haveparticularly significant thread heights making their ability to threadthemselves into the bone particularly effective.

FIGS. 46A, 46B and 46D, show openings at the trailing end of the implantfor receiving opposed screws that may be oriented from the implant intoeach of the adjacent vertebral bodies. These screws enter the implantthrough the trailing end and the threaded shafts of the screws passthrough openings in the opposite upper and lower vertebral body engagingsurfaces of the implants. Shown in FIGS. 50-53 is a cut away throughimplant 900 of FIG. 46B. This is a cross section through themid-longitudinal axis of implant 900 and the adjacent vertebral bodies.FIGS. 47A and 47B show a screw driver 880 and FIG. 51 shows driver 880driving a bone screw 842 through bone screw receiving hole 930 and out842 through lower vertebrae engaging surface 908 into adjacent vertebralbody V₂.

The present invention includes the use of any bone screws for thisdescribed purpose. In preferred embodiments, structure is provided toblock the bone screws from disengaging from the implant or backing out.The screws may be rigidly locked to the implant or may be prevented frombacking out in a manner that still allows for some relative motionbetween the screws and the implant. The latter may be beneficial foranticipating and allowing for some settling of the vertebral bodiestowards the disc space. In use, as shown in FIG. 51, the driver 880 isassembled to the screw 842 thereby compressing the head portion of thescrew. The screw is then introduced through the trailing end of theimplant and directed into the body of one of the adjacent vertebraepassing out of an opening adapted for that purpose in one of theopposite vertebrae engaging surfaces of the implant. The head of thescrew 842 is too large to pass through the opening in the implant, andyet is free to spin against the implant itself making it possible to lagthe screw, or that is to draw the body of the vertebra to the implantand to generate compressive load between the implant and the vertebralbody.

FIGS. 46A and 46C show a preferred embodiment of implant800. The lateralside wall and medial side wall have a distance therebetween defining animplant width transverse to the implant height. The width of implant 800is less than its height along at least a portion of its length. Themedial side wall is preferably configured to be positioned in closeproximity to at least implant 900 such that the combined width ofimplants 800, 900 is less than the combined height of those implants.

Implant 800 is similar to implant 900, but differs from implant 900 inthat while the lateral sides of implants 800 and 900, respectively, arethe same and in this example convex, the medial side of implant 800 hasbeen relieved so as to allow for the convex medial side of implant 900to protrude therein. Alternatively, the medial side of implant 800 canbe relieved, in part absent, and/or concave.

Implant 800 also has at the medial side a convexity as shown by thecontour of trailing support wall 804. In a preferred embodiment, leadingsupport wall 802 may similarly be concave. And further a portion of themedial side wall is absent so as to allow for the protrusion of implant900 therein.

As shown in FIG. 46B, thread 922 of implant 900 may have a generallyconstant outer diameter. Inasmuch as the body of implant 900 isgenerally conical such that it tapers from the larger trailing end 904to the smaller leading end 902, the height of thread 922 relative to thebody increases from trailing end 904 to leading end 902. Thus, while theouter diameter of the threads remains generally constant, the height ofthe thread increases from trailing end 904 to leading end 902. This issimilarly true for implant 800.

In a preferred embodiment of implants 800, 900 the start of the externalthread about the perimeter of the implant is precisely indexed such thatif the surgeon knows the depth of the bore created, he may select animplant of the desired length being less than or equal to the depth ofthe bore created and by starting the insertion of the implant in apreferred rotational alignment such as the desired final rotationalalignment the implant when threaded in fully will come to rest such thattrailing end 804, 904 will be correctly rotationally aligned so that thescrew receiving holes 834, 836, 934, 936 will be oriented correctlytowards the adjacent vertebral bodies while the profile of trailing ends804, 904 will correspond to the contour of the anterior vertebral body.

By way of example, for a bore measured to receive a 30 millimetermaximum length implant having a pitch of three millimeters as anexample, the start of the thread at the implant leading end could beindexed such that the implant could be introduced rotationally orientedexactly as desired for the final positioning. Then, by making tencomplete revolutions of three millimeters each the implant wouldassuredly come to rest with trailing wall 804 appropriately oriented andeither be flush with the anterior vertebral cortices, or minimallycounter-sunk to exactly the extent to which the surgeon caused theimplant to enter the bore prior to initiating rotation. As previouslymentioned, trailing end 804 of implant 800 could be rotationallyasymmetrical, but nevertheless be symmetrical from side-to-side, suchthat each of the sides of the implant would be less protuberantposteriorly than a point along the mid-longitudinal axis such that theimplant could be correctly inserted in increments of less than or equalto 180 degrees of rotation.

As shown in FIGS. 48 and 49, screw 842 has a threaded shaft 848 having aleading end 844, a tip 846, and an opposite trailing end 852. Shaft 848has a thread form for engaging bone. Trailing end 852 has a screw headhaving an enlarged portion 856 having a diameter greater than the outerdiameter of the threaded portion of shaft 848. The screw head has acruciate recess 861 for receiving the end 890 of screw driver 880.

FIG. 46B shows a front view of an embodiment of the present inventionwith implants 800, 900 properly implanted across the disc space betweenadjacent vertebral bodies V₁ and V₂. Openings 820,920 also are adaptedto receive a screw device to link the implant to other implants, to astaple, or to receive a locking screw to lock bone engaging screws tothe implant as disclosed in Michelson U.S. patent application Ser. No.08/926,334 incorporated herein by reference. As shown in the preferredembodiment of the present invention, trailing ends 804 and 904 ofimplants 800 and 900, respectively, preferably are rotationallyasymmetrical about the longitudinal axes of the implants such that thedesignated medial side of each of the implants has a length greater thanthe lateral sides of the same implants. Trailing ends 804, 904preferably are structured to have a lesser length along their lateralsides than through the mid-longitudinal axis and are preferablycontoured so as to sit on the anterior rims of the vertebral bodieswithout protruding dangerously therefrom as set forth in pendingMichelson application Ser. No. 09/263,266 incorporated herein byreference. In another embodiment of the present invention, the trailingends of the implants can have a maximum length along themid-longitudinal axis greater than the length along either of the medialand lateral sidewalls so that the bone screw receiving holes can beoriented towards the adjacent vertebral bodies in half rotationincrements rather than requiring a full rotation. While for implant 900this would require no other modification than as described for thetrailing end, in regard to implant 800 each of the lateral and medialside walls would have to be relieved to allow for the receipt of theperimeter of implant 900 within the maximum perimeter of implant 800.

In each of the examples of the present invention as offered, it isunderstood that the invention is limited to screws that are appropriatefor their intended purpose and thus related to the overall size of theimplant as it relates to the region of the spine for which it isconfigured for implantation.

Specifically, the screws of the present invention have the followingpreferred size. When for use in the lumbar spine, the screws have atleast partially threaded shafts having outer diameters (major diameter)not less than 4.8 mm and not greater than 10 mm with 6 mm to 8 mmgenerally preferred. A preferred root diameter is at least 1.5 mm lessthan the outer diameter and most preferably 2.5 mm to 5 mm. When thescrew is used from anterior to posterior, a length of from 10 mm to 40mm is preferred with 20 mm to 30 mm being more preferred. When the screwis used in a lateral approach, a length of from 10-50 mm is preferredwith 25-35 mm being more preferred.

The screws preferably have head portions having an outside dimensiongenerally equal to or greater than the outer diameter of the thread ofthe threaded shaft. An exception is where the head has an outwardlyfacing machine thread and the shaft has a cancellous thread with theturns or pitch of the thread being spaced apart to exceed the wallthickness of that portion of the implant adapted to retain the screwhead.

Further, the screws preferably have pointed leading ends and are selftapping with cutting flutes and have an interrupted thread at theirleading end. The screws preferably have a smooth shaft portionproximally near the head. All screws preferably have at their trailingends adapted for cooperatively engaging a screw driver.

Screws used in the cervical spine vary from screws used in the lumbarspine in that a preferred major diameter is 3.5-5.5 mm with 4.0 mm to5.0 mm being more preferred. A preferred length is from 8-20 mm with12-16 mm being more preferred.

Preferred screws for use in the thoracic spine vary from screws used inthe lumbar and cervical spine in that a preferred thread has an outerdiameter from 4-8 mm with 5-7 mm being more preferred. The screws havinga length of from 10 mm to 30 mm with a length of approximately 20 mmplus or minus 5 mm being more preferred.

It is believed that the operation and construction of the presentinvention will be apparent from the foregoing description and, while theinvention shown and described herein has been characterized asparticular embodiments, changes and modifications may be made thereinwithout departing from the spirit and scope of the invention, which islimited only by the scope of the claims.

What is claimed is:
 1. An apparatus comprising: an interbody spinalfusion implant for surgical implantation at least in part within a discspace between two adjacent vertebral bodies in a segment of a humanspine, said implant comprising a leading end for entry into the spine, atrailing end opposite said leading end, and a length therebetween; andupper and lower portions for contacting each of the adjacent vertebralbodies when positioned therein, each of said upper and lower portionshaving at least one opening adapted to communicate with one of theadjacent vertebral bodies, said openings of said upper and lowerportions being in communication with one another and adapted forpermitting for the growth of bone from adjacent vertebral body toadjacent vertebral body through said implant, each of said upper andlower portions having at least one screw hole passing therethroughproximate said trailing end; bone screws adapted for placement throughsaid screw holes of said upper and lower portions and into each of theadjacent vertebral bodies adjacent the disc space to be fused and intowhich said implant is adapted to be positioned; and a lock adapted tocooperatively engage said implant, said lock capable of beingpre-installed to said implant prior to insertion of at least one of saidbone screws into said at least one of said screw holes, said lock beingmovable from a first position to a second position, said lock beingconfigured so as to permit insertion of at least one of said bone screwsinto at least one of said screw holes, when in said first position andso as to cover at least a portion of at least one of said bone screwsinserted in at least one of said screw holes when said lock is in saidsecond position.
 2. The apparatus of claim 1, wherein said implantfurther comprises a hollow interior for holding bone growth promotingmaterial, said hollow interior being in communication with said at leastone opening in each of said upper and lower portions.
 3. The apparatusof claim 1, wherein said implant has means for retaining a portion ofsaid bone screw to prevent said bone screw from passing entirely throughsaid screw hole into which it is adapted to be inserted.
 4. Theapparatus of claim 1, wherein said screw holes are opposed anddivergently angled to one another.
 5. The apparatus of claim 1, whereinsaid screw holes are angled between 25 and 75 degrees from amid-longitudinal axis of said implant.
 6. The apparatus of claim 1,wherein said screw holes include retaining seats peripheral to saidscrew holes adapted to receive and to block the passage of at least aportion of said bone screws to be inserted therethrough.
 7. Theapparatus of claim 1, wherein said screw holes are opposed anddivergently angled and extend from said trailing end and through saidupper and lower portions.
 8. The apparatus of claim 7, wherein saidscrew holes extending from said trailing end are configured so as to beadapted to be oriented towards the adjacent vertebral bodies in halfrotation increments of said implant.
 9. The apparatus of claim 1,wherein said bone screws and said screw holes cooperate to allow forangular motion of said bone screws relative to the implant.
 10. Theapparatus of claim 1, wherein each screw hole has a longitudinal axisand is formed to retain a respective bone screw in a position in whichthe longitudinal axis of said respective bone screw is aligned with thelongitudinal axis of said screw hole.
 11. The apparatus of claim 1,wherein at least one of said screw holes has an upper diameter portionand a smaller lower diameter portion to prevent a bone screw beingplaced in said one of said screw holes from passing entirely throughsaid at least one of said screw holes.
 12. The apparatus of claim 1,wherein at least a portion of said bone screws are adapted to pass fromsaid interior of said implant through said screw holes and into theadjacent vertebral body to anchor said implant to the adjacent vertebralbody.
 13. The apparatus of claim 1, wherein said bone screws are lagscrews.
 14. The apparatus of claim 1, wherein said bone screws areappropriately sized and configured to function for their intendedpurpose.
 15. The apparatus of claim 1, wherein said bone screws aresized and configured for use in the cervical spine.
 16. The apparatus ofclaim 1, wherein said bone screws are sized and configured for use inthe lumbar spine.
 17. The apparatus of claim 1, wherein said bone screwsare sized and configured for use in the anterior aspect of the spine.18. The apparatus of claim 1, Wherein said bone screws have a sharpdistal end.
 19. The apparatus of claim 1, wherein said bone screws havea distal end and a head opposite said distal end, said head beingadapted to engage a driving instrument.
 20. The apparatus of claim 1,wherein said bone screws are selected from a series of screws havingdifferent lengths.
 21. The apparatus of claim 1, wherein said bonescrews have a head, a shaft attached to said head and terminating at atip, said shaft having a thread, said head having a transverse crosssectional dimension greater than the transverse cross sectionaldimension of said shaft, said head being configured to cooperativelyengage a driver instrument.
 22. The apparatus of claim 21, wherein saidhead of at least one of said bone screws has a first upper diametersection and a smaller lower diameter section.
 23. The apparatus of claim21, wherein said head of at least one of said bone screws has engagementmeans for engagement with a screw-driving tool.
 24. The apparatus ofclaim 23, wherein said engagement means is an irregular recess.
 25. Theapparatus of claim 1, wherein said bone screws are within the lengthbetween said leading and trailing ends when positioned through saidscrew holes.
 26. The apparatus of claim 1, wherein said bone screw is atleast in part made of a resorbable material.
 27. The apparatus of claim1, wherein said bone screw comprises a metal suitable for humanimplantation.
 28. The apparatus of claim 1, wherein at least one of saidbone screws has a head dimensioned to achieve an interference fit with arespective one of said screw holes.
 29. The apparatus of claim 1,wherein at least one of said bone screws has a shaft dimensioned toachieve an interference fit with a respective one of said screw holes.30. The apparatus of claim 1, wherein said bone screws are self-tapping.31. The apparatus of claim 30, wherein fluting interrupts at least twothread turns proximate a bone screw tip.
 32. The apparatus of claim 1,wherein said trailing end of said implant is adapted to receive bonescrews and to transmit at least a portion of the screws through saidupper and lower portions so as to engage at least one each into each ofthe vertebral bodies adjacent the disc space.
 33. The apparatus of claim1, wherein said trailing end of said implant includes retaining seatsperipheral to said screw holes adapted to receive and to block thepassage of at least a portion of said screws to be insertedtherethrough.
 34. The apparatus of claim 1, wherein said trailing end ofsaid implant is configured to cooperatively engage an implant driver.35. The apparatus of claim 1, wherein said lock has a bearing surfacefor bearing against a portion of at least one of said bone screws whensaid lock is in said second position.
 36. The apparatus of claim 1,further comprising a recess for receiving said lock for locking at leastone of said bone screws to said implant.
 37. The apparatus of claim 36,wherein said recess has a threaded portion.
 38. The apparatus of claim1, wherein said lock comprises a threaded member.
 39. The apparatus ofclaim 38, wherein said lock comprises a screw having a head portion anda threaded shaft.
 40. The apparatus of claim 1, wherein said lock coversat least a portion of said bone screw receiving hole.
 41. The apparatusof claim 1, wherein said lock allows for angular motion of said bonescrews relative to the implant.
 42. The apparatus of claim 1, whereinsaid lock is a set screw.
 43. The apparatus of claim 1, wherein saidlock is a screw.
 44. The apparatus of claim 1, wherein said lock is arivet.
 45. The apparatus of claim 1, wherein said bone screws and saidlock do not project beyond said trailing end of said implant when saidimplant is installed.
 46. The apparatus of claim 1, wherein at least oneof said screw holes has a reduced diameter lower portion and anincreased diameter upper portion, and said lock engages said increaseddiameter upper portion of one of said screw holes to lock one of saidbone screws to said implant, said lock being adapted to bear against oneof said bone screws when in one of said screw holes.
 47. The apparatusof claim 1, wherein said lock is adapted to lock a plurality of saidbone screws to said implant.
 48. The apparatus of claim 1, wherein saidlock has at least two segments removed therefrom, each of said at leasttwo segments corresponding to a different screw hole whereby movement ofsaid lock from said first position to said second position causes saidlock to bear against at least a portion of the bone screws in said twoscrew holes.
 49. The apparatus of claim 1, wherein said bone screw has ahead with an irregular depression in the top of said head for engagementwith a screwdriver; and said lock has a head with an irregulardepression in said head for engagement with a screwdriver, whereby bothsaid heads of said bone screw and said lock may be engaged by the samescrewdriver.
 50. The apparatus of claim 1, wherein said upper and lowerportions are parallel to one another.
 51. The apparatus of claim 1,wherein said upper and lower portions are convergent to one another. 52.The apparatus of claim 1, wherein said upper and lower portions aregenerally planar surfaces.
 53. The apparatus of claim 1, wherein saidupper and lower portions are opposed arcuate portions.
 54. The apparatusof claim 1, wherein at least a portion of said upper and lower portionsare arcuate along at least a portion of their length.
 55. The apparatusof claim 54, wherein said opposed arcuate portions form at least aportion of a cylinder along the length of said implant.
 56. Theapparatus of claim 54, wherein said opposed arcuate portions form anangular orientation relative to one another.
 57. The apparatus of claim54, wherein said opposed arcuate portions form a cylindrical shape. 58.The apparatus of claim 54, wherein said opposed arcuate portions form afrusto-conical shape.
 59. The apparatus of claim 54, wherein each ofsaid opposed arcuate portions have at least a portion of a threadthereon.
 60. The apparatus of claim 59, wherein said thread has peaksand said peaks are relatively constant along the length of said implantso that the outer diameter of said implant is generally constant. 61.The apparatus of claim 59, wherein said thread has a constant height asmeasured from said opposed arcuate portions.
 62. The apparatus of claim59, wherein said thread of said implant is interrupted.
 63. Theapparatus of claim 59, wherein said thread of said implant has a sharppointed profile at said leading end and progresses to a thicker and moresquared profile at said trailing end.
 64. The apparatus of claim 59,wherein said thread of said implant is a projection generally orientedperpendicular to a mid-longitudinal axis.
 65. The apparatus of claim 59,wherein said thread of said implant forms a single helix.
 66. Theapparatus of claim 1, wherein each of said upper and lower portions haveat least one bone engaging projection thereon.
 67. The apparatus ofclaim 66, wherein said projection is a fin.
 68. The apparatus of claim66, wherein said projection a ridge.
 69. The apparatus of claim 1,wherein at least one of said leading and trailing ends is open to allowaccess to said hollow interior.
 70. The apparatus of claim 69, furthercomprising a cap for closing at least one of said ends of said implant,said cap having an exterior surface and an interior surface.
 71. Theapparatus of claim 70, wherein said cap includes a threaded portion forthreadably engaging said leading end of said implant.
 72. The apparatusof claim 70, wherein said cap is perforated.
 73. The apparatus of claim1, wherein said implant comprises an artificial material other thanbone.
 74. The apparatus of claim 1, wherein said implant is made of anartificial material that is stronger than bone.
 75. The apparatus ofclaim 1, wherein said implant is made of an artificial material that isharder than bone.
 76. The apparatus of claim 1, wherein said implantcomprises bone.
 77. The apparatus of claim 76, wherein said boneincludes cortical bone.
 78. The apparatus of claim 76, wherein bonepromoting material is compressively loaded into said implant.
 79. Theapparatus of claim 1, wherein said implant comprises bone growthpromoting material.
 80. The apparatus of claim 79, wherein said bonegrowth promoting material is selected from one of bone morphogeneticprotein, hydroxyapatite, and genes coding for the production of bone.81. The apparatus of claim 1, wherein said implant is treated with abone growth promoting substance.
 82. The apparatus of claim 1, whereinsaid implant is a source of osteogenesis.
 83. The apparatus of claim 1,wherein said implant is at least in part bioabsorbable.
 84. Theapparatus of claim 1, wherein said implant comprises a plastic material.85. The apparatus of claim 1, wherein said implant comprises a ceramicmaterial.
 86. The apparatus of claim 1, wherein said implant is formedof a porous material.
 87. The apparatus of claim 1, wherein said implantis formed of a material that intrinsically participates in the growth ofbone from adjacent vertebral body to adjacent vertebral body throughsaid implant.
 88. The apparatus of claim 1, in combination with achemical substance to inhibit scar formation.
 89. The apparatus of claim1, in combination with a fusion promoting substance.
 90. The apparatusof claim 89, wherein said fusion promoting substance includes at leastone of bone, bone morphogenetic protein, hydroxyapatite, and geneticmaterials coding for the production of bone.
 91. The apparatus of claim1, in combination with an orthopedic device for use in spinal surgery.92. The apparatus of claim 91, wherein said orthopedic device is a boneremoval device for preparing a space between and at least in part intothe adjacent vertebral bodies.
 93. The apparatus of claim 92, whereinsaid bone removal device is one of a drill and a mill.
 94. The apparatusof claim 91, wherein said orthopedic device is a screw driver forinserting bone screws.
 95. The apparatus of claim 91, wherein saidorthopedic device is an implant driver for inserting said spinalimplant.